I'm not sure why mediums, Allied or Axis, have the ability to crush in the first place, to be frank. Is it really necessary?
Is directional cover necessary?
Crush is just another element of gameplay. And it makes sense for the same reason infantry cannot damage armor with small arms fire unlike many other RTS games.
PS This topic doesn't even make sense since now both Axis factions mainline infantry have vehicle snares. So you're actually going to be able to better defend your blobs from crushes than before when OKW had no snare and Cromwells / M10s could just speed in, shake off Shrek shots, and murder everything.
Another option is to just.... ya know, not blob so the crush is less of a threat.